MacBook Retina charger

Hi;
Just ordered the wife a 12.9" iPad Pro.
I've been reading that using the rMacBook's 29W charger, along with an Apple USB C to Lightning connector, charges the iPad Pro faster, so I ordered those two items as well.
My question is; can I use that setup (29W charger + USB C to Lightning cable) to charge an iPhone also?
I know that using the 12W charger is fine, as the iPhone simply takes what it needs, but would it also be safe to charge using the 29W charger?
Anyone here using that setup with an iPhone?
Thanks.

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